Three major areas of research are under investigation: 1) A comparison of the chemical structures of the two forms of actin (Actin I and Actin II) which have been identified in platelets. 2) Interaction of one or both forms of actin with spectrin which has been identified in this laboratory as being present in platelets. 3) Function of a Ca ions binding protein which has been isolated and characterized in this laboratory. These investigations are designed to understand the role of Ca ions, actin, spectrin and myosin in the physiological functioning of platelets. BIBLIOGRAPHIC REFERENCES: Sato, T., Herman, L., Chandler, J., Detwiler, T.C., and Stracher, A., Localization of Ca ions in platelets, J. Histo. and Cyto. 23, 103 (1975). Abramowitz, J., Detwiler, T.C., and Stracher, A., A second form of Actin; Platelet microfilaments depolymerized by ATP and divalent cations, Arch. Biochem. and Biophys., 167, 230 (1975).